Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. For example, Spinal Cord Stimulation (SCS) techniques, which directly stimulate the spinal cord tissue of the patient, have long been accepted as a therapeutic modality for the treatment of chronic neuropathic pain syndromes, and the application of spinal cord stimulation has expanded to include additional applications, such as angina pectoralis, peripheral vascular disease, and incontinence, among others. Spinal cord stimulation is also a promising option for patients suffering from motor disorders, such as Parkinson's Disease, Dystonia and essential tremor.
An implantable SCS system typically includes one or more electrode-carrying stimulation leads, which are implanted at a stimulation site in proximity to the spinal cord tissue of the patient, and a neurostimulator implanted remotely from the stimulation site, but coupled either directly to the stimulation lead(s) or indirectly to the stimulation lead(s) via a lead extension. The neurostimulation system may further include a handheld patient programmer to remotely instruct the neurostimulator to generate electrical stimulation pulses in accordance with selected stimulation parameters. The handheld programmer may, itself, be programmed by a technician attending the patient, for example, by using a Clinician's Programmer (CP), which typically includes a general purpose computer, such as a laptop, with a programming software package installed thereon.
Thus, programmed electrical pulses can be delivered from the neurostimulator to the stimulation lead(s) to stimulate or activate a volume of the spinal cord tissue. In particular, electrical stimulation energy conveyed to the electrodes creates an electrical field, which, when strong enough, depolarizes (or “stimulates”) the neural fibers within the spinal cord beyond a threshold level, thereby inducing the firing of action potentials (APs) that propagate along the neural fibers to provide the desired efficacious therapy to the patient.
As discussed, SCS may be utilized to treat patients suffering from chronic neuropathic pain. To this end, electrical stimulation is generally applied to the dorsal column (DC) nerve fibers, which is believed to inhibit the perception of pain signals via the gate control theory of pain by creating interneuronal activity within the dorsal horn that inhibits pain signals traveling from the dorsal root (DR) neural fibers that innervate the pain region of the patient up through the spinothalamic tract of the spinal cord to the brain. Consequently, stimulation leads are typically implanted within the dorsal epidural space to provide stimulation to the DC nerve fibers. Such techniques of treating pain may be beneficial for some patients initially, but it has decreasing efficiency over time. This may be because the natural neural interconnections may be minimally present in some patients, or because the natural neural interconnections may be rendered ineffective by the pathological condition.
Some prior art techniques, such as those disclosed in U.S. Patent Publication Nos. 2005/0055065 and 2004/0162594, propose directly stimulating the spinothalamic tract to inhibit the pain signals from traveling up the spinothalamic tract to the brain. However, the spinothalamic tract in these cases are subdurally stimulated, which requires a more difficult, complex, and risky surgical procedure.
Although it would be desirable to epidurally stimulate the spinothalamic tract, various sensitive neural structures, including the dorsal root (DR) nerve fibers and ventral root (VR) nerve fibers, are in close proximity to or even overlap the spinothalamic tract. As a result, epidural stimulation of the spinothalamic tract to treat chronic neuropathic pain may be difficult to accomplish without also inadvertently creating side-effects, e.g., in the form of uncomfortable muscle contractions and pain resulting from the inadvertent stimulation of the DR and/or VR nerve fibers.